This is great, I will definitely look into Wi2 300 on my next Japan trip. I too, stayed at Shinagawa Prince and went to the Yahoo Cafe every couple of days to check Facebook, email and travel info. I did manage to get find free wifi signal (though slow speed), between McDonalds and the ramp leading up to Shinagawa Hotel.
I would recommend the Dormy Inn chain. I stayed in the one in Kanazawa at an excellent price, the usual size for a single but very clean room. It had a sauna, free guest computers, sauna, coin laundry (but I couldn't figure out the Japanese controls) and did I mention SAUNA!?!

Next time, I'll skip Shinagawa Prince and go to Dormy Inn ^